1. Field of said Invention
The present invention relates generally to a printing plate lock-up apparatus for a plate cylinder in a printing press, such as a rotary press. More specifically, the invention relates to a printing plate lock-up apparatus of the type having a groove opening on the periphery of the plate cylinder and extending in a longitudinal direction, and an engaging member rotating within the groove for engaging with a printing plate.
2. Description of the Related Art
In the field of rotary presses, various constructions of printing plate lock-up apparatus of the type having a groove opening on the periphery of the plate cylinder and extending in longitudinal direction and an engaging member rotating within the groove for engaging with a printing plate, have been known. For example, Japanese Examined Utility Model Publication No. 62-9100, Japanese Examined Patent Publication No. 2-193 and Japanese Unexamined Patent Publication No. 5-42665 disclose a printing plate lock-up apparatus of the type set forth above.
The printing plate lock-up apparatus disclosed in the above-identified Japanese Examined Utility Model Publication No. 62-9100 includes a groove opening in the longitudinal direction of a plate cylinder. The edge portion of the groove serves for hooking a turned back portion of a printing plate located at the leading side with respect to a direction of rotation of the plate cylinder during printing. A printing plate tightening bar is disposed within the groove in a rotatable fashion and has an engaging claw for engaging with another turned back portion of the printing plate located at the trailing end side. A toggle switching mechanism is interposed between the center of rotation of the bar and the center of the plate cylinder for switching a symmetric angular displacement position of the bar in two directions, and an operation means is provided for externally driving the bar for rotation.
On the other hand, the printing plate lock-up apparatus disclosed in the above-identified Japanese Examined Patent Publication No. 2-193 has a groove opening in the longitudinal direction of a plate cylinder. The edge portion of the groove serves for hooking a turned back portion of a printing plate located at the leading side with respect to a direction of rotation of the plate cylinder during printing. A cam member is disposed within the groove in a rotatable fashion. The cam member is provided with a curved peripheral surface having a radius of curvature substantially corresponding to the radius of curvature of the bottom of the groove. The groove has an outer side portion having a greater volume than that defined by the bottom portion. The cam disposed within the bottom portion of the groove is provided with a cut-out extending substantially the whole longitudinal length of the bottom surface of the bottom portion of the groove. Within the upper portion of the groove, a spring has a substantially U-shaped configuration and a hooked upper end for engaging with the turned back edge of the printing plate in the rotating direction of the plate cylinder during printing. The spring cooperates with a toggle member which has a lower end portion of complementary configuration to the cam member so as to cause a rocking motion of the spring and to maintain the spring at a rocked position. Therefore, depending upon the rotating direction of the cam member, the rocking, direction of the spring can be alternated.
Japanese Unexamined Patent Publication No. 5-42665 discloses the printing plate lock-up apparatus including a groove opening in a longitudinal direction of a plate cylinder. The edge portion of the groove serves for hooking a turned back portion of a printing plate located at the leading side with respect to a direction of rotation of the plate cylinder during printing. A bar is rotatably disposed within the groove. A resilient member having a bent engaging portion is mounted on the bar. The engaging portion of the resilient member is adapted to engage with the turned back portion of the printing plate at the trailing side with respect to the rotating direction of the plate cylinder during printing. An operation means is provided for operating the bar for rotation such that the engaging portion of the resilient member is displaced toward the edge engaging with the leading end side of the printing plate, and for maintaining a predetermined angular displacement phase of the bar.
Here, as can be appreciated, the printing plate lock-up apparatus is the apparatus for loading the printing plate on the plate cylinder. Failure of the printing plate lock-up apparatus directly results in a shut down of the overall printing press or rotary press. Therefore, it has been strongly required that the printing plate lock-up apparatus is easy to maintain and repair.
To this end, the printing plate lock-up apparatus disclosed in the above-mentioned Japanese Examined Utility Model Publication No. 62-9100 constructs the overall mechanism of the apparatus as an integral block having a surface matching with the peripheral surface of the plate cylinder. The integral block is disposed within a relatively large groove so that whole block can be replaced when failure occurs.
Accordingly, though it may facilitate repairing, the disclosed apparatus requires a large number of parts, and further requires high surface precision at the mating surfaces for installation of the integral block, thus resulting in a high production cost.
Also, since a relatively large groove has to be formed through a machining process, a difficulty is encountered in an application for a plate cylinder having a relatively thin wall thickness, such as a divided cylinder used in newspaper printing. The divided cylinder is disclosed in U.S. Pat. No. 5,267,512.
The printing plate lock-up apparatus disclosed in Japanese Examined Patent Publication No. 2-193 permits removal and installation of the cam member and the bar-shaped toggle member through the opening end of the groove opening to the periphery of the plate cylinder. At the occurrence of failure, the cam member and the bar-shaped toggle member are removed from and re-installed in the groove through the opening end.
Therefore, this apparatus also facilitates repairing. However, two members, i.e., the cam member and the bar-shaped toggle member, are required to be disposed within the groove, and the toggle member must be coupled with the spring. Thus, the number of parts is not satisfactorily small. Furthermore, since the groove has a relatively complicated cross section, machining of such a groove is not easy resulting in a high production cost.
Furthermore, since the shown apparatus requires the groove to have two portions, i.e., the upper portion and the bottom portion, sufficient depth of the groove is inherently required. Therefore, the shown apparatus is not practically possible to apply for the plate cylinder having a relatively thin wall, such as the divided cylinder in the newspaper printing press.
On the other hand, the apparatus disclosed in Japanese Unexamined Patent Publication No. 5-42665 requires only a bar member mounting the resilient member to be disposed within the groove having a substantially semi-circular cross section for rotation thereabout. This permits the construction of the groove to be simple and small.
Therefore, the shown apparatus will be applicable for the plate cylinder having a thin wall, such as the divided cylinder. Also, because of its simple construction, the production cost can be low.
However, the shown apparatus requires parallel movement of the bar member relative to the groove in installation and removal. Therefore, installation and removal of the bar member into and from the groove is not satisfactorily easy to allow a quick repair.